A QUANTITATIVE INVESTIGATION OF PHASE-FORMATION DURING ANNEALING OF COLD-EXTRUDED ELEMENTAL POWDER MIXTURES TI-48 AT-PERCENT AL AND TI-48 AT-PERCENT AL-2 AT-PERCENT CR

Formation processes of titanium aluminides during annealing of cold-ex truded elemental powder mixtures, Ti-48 at.% Al and Ti-48 at.% Al-2 at .% Cr, have been quantitatively investigated. The reaction between Ti and Al to form TiAl and Ti3Al passes through several non-equilibrium s tates, during which Al3Ti and Al2Ti are formed. The volume fraction of Al3Ti decreases exponentially with time, between 700 and 1000-degrees -C. The formation and dissolution of Al2Ti can be approximated by a pa rabola of third order on the logarithmic time scale. During the format ion of Al2Ti the volume fraction of TiAl remains relatively constant. As dissolution of Al2Ti begins, the volume fraction of TiAl increases up to the equilibrium value. The volume fraction of Ti3Al continuously decreases from the initial concentration to the equilibrium value. Wi th increasing temperature, the reaction processes are accelerated. Alt hough the phase formation processes are not significantly altered by C r additions, the reaction speed is reduced by about a factor of three. The effect of Cr on the reaction is discussed.